Phagocytosis and pinocytosis are different mechanisms of endocytosis, but what is the difference between them? BiologyWise gives you a detailed account of phagocytosis vs. pinocytosis.
Biological Pacman
Phagoptosis is the process by which a cell is phagocytosed by another cell. This process usually takes place when the other cell is stressed, damaged, old, cancerous, infected by virus, or foreign.
Cells take in large polar molecules, protein, sugars, etc., through their hydrophobic cell membrane by the process of endocytosis. This is an energy-consuming process. It is required by the cell to perform a number of functions such as recycling the surface receptors, importing extracellular molecules into the cell, as well as engulfing and degrading various pathogenic agents from the surrounding of the cell.
An endocytic pathway involves internalization of molecules via invagination of the cell membrane and then pinching off to form the early endosome. This early endosome forms the late endosome, which then forms the lysosome. Endocytosis can be classified into three types: phagocytosis, pinocytosis, and receptor-mediated endocytosis. In receptor-mediated endocytosis, there is internalization of molecules that bind to cell receptors specific for that molecules.
We will discuss phagocytosis and pinocytosis in detail now.
What is the Difference Between Phagocytosis and Pinocytosis?
Although phagocytosis and pinocytosis are basic mechanisms of endocytosis, there are a few differences between them.
Definition
Phagocytosis: It is the internalization of larger, extra-cellular, solid particles, such as bacteria, from the surrounding medium. It is sometimes referred to as ‘cell eating’.
Pinocytosis: It is the internalization of extracellular fluids along with its solute molecules from the surrounding medium. It is sometimes referred to as ‘cell drinking’.
| Mechanism of Internalization | |
| ● In this process, there is formation of feet-like processes called pseudopodia. These pseudopodia are extended around the molecule to be internalized and is taken in by the cell. This process is called engulfment. | ● In this process, there is infolding of the cell membrane along with the extracellular fluid and the solute particles dissolved in it. This process is called invagination. |
| Type of Cells | |
| ● This process is performed only by special type of phagocytic cells. In higher animals, it is largely concerned with the elimination of foreign materials and pathogens. | ● This process is performed by all cells. It is usually responsible for the uptake of solute molecules and smaller nutrients from the surrounding. |
| Specificity | |
| ● Phagocytic cells are usually very specific in the particles they engulf. | ● Pinocytic cells are usually not specific in the molecules they invaginate. |
| Nature of Particles Internalized | |
| ● Large molecules are internalized by phagocytosis; these molecules are broken down by hydrolytic enzymes after internalization. | ● In pinocytosis, already-broken-down dissolved molecules are internalized. |
| Type of Endosome | |
| ● The molecules are engulfed to form vesicles; these vesicles are called phagosomes. They are larger than 0.75 µm in diameter. | ● The vesicles formed by this process are called pinocytic vesicles or pinosomes and are much smaller in size, about 0.5-5 µm in diameter. |
| Expenditure of Energy | |
| ● A large amount of energy is given off in this process. | ● Some amount of energy is generated in the form of ATP molecules, in the pinocytosis of smaller lipids. |
| Examples | |
| ● Certain protozoans, such as amoeba, engulf food by the process of phagocytosis. ● In the immune system of mammals, certain foreign particles like pathogens are internalized by specialized phagocytic cells such as macrophages. |
● Cells take up hormones from their surroundings by this process. ● The epithelial cells of the intestines and the human ovum take up nutrients with the help of this mechanism. ● Root hair cells in plants take water and solute molecules from the soil by pinocytosis. |